Thiopronin reduces the frequencies of neocarzinostatin-induced chromosomal aberrations and sister chromatid exchanges in Chinese hamster ovary cells

Collateral sensitivity of multidrug-resistant cells to the orphan drug tiopronin

A major challenge in the treatment of cancer is multidrug resistance (MDR) that develops during chemotherapy. Here we demonstrate that tiopronin (1), a thiol-substituted N-propanoylglycine derivative, was selectively toxic to a series of cell lines expressing the drug efflux pump P-glycoprotein (P-gp, ABCB1) and MRP1 (ABCC1). Treatment of MDR cells with 1 led to instability of the ABCB1 mRNA and consequently a reduction in P-gp protein, despite functional assays demonstrating that tiopronin does not interact with P-gp. Long-term exposure of P-gp-expressing cells to 1 sensitized them to doxorubicin and paclitaxel, both P-gp substrates. Treatment of MRP1-overexpressing cells with tiopronin led to a significant reduction in MRP1 protein. Synthesis and screening of analogues of tiopronin demonstrated that the thiol functional group was essential for collateral sensitivity while substitution of the amino acid backbone altered but did not destroy specificity, pointing to future development of targeted analogues.

The protective role of thiola and soybean seeds against the genotoxicity induced by potassium dichromate in mice

The genotoxic potential of potassium dichromate (K(2)Cr(2)O(7)) was evaluated in vivo in mice using different mutagenic end points. Chromosomal aberrations in bone-marrow and spermatocytes as well as sperm abnormalities in the tested mice were determined. The doses used were 3, 6, 12 mg K(2)Cr(2)O(7)kg(-1) body weight which correspond to 1/16, 1/8, 1/4 the experimental LD(50), respectively. The protective roles of i.p. injection with thiola (a synthetic sulfhydryl compound) at 20 mg kg(-1) body weight and feeding treatment with soybean seeds (30% of the diet) were also studied. For chromosomal aberration analysis, subacute treatment for a period of 3 weeks were performed. All the tested doses of K(2)Cr(2)O(7) induced a statistically significant increase in the percentage of chromosomal aberrations in both somatic and germ cells with dose and time relationships. The percentage of the induced chromosomal aberrations was significantly minimized in all groups of mice i.p. treated with thiola or fed soybean seeds during the period of treatment. Potassium dichromate also induced a significant increase (P<0.01) in the percentage of abnormal sperms at the doses 6 and 12 mg kg(-1) body weight. Such percentage reached 7.52+/-0.45, 5.50+/-0.53 and 4.28+/-0.45 in mice treated with the highest tested dose of K(2)Cr(2)O(7), K(2)Cr(2)O(7) and thiola; K(2)Cr(2)O(7) and soybean, respectively compared with 2.14+/-0.33 for the control. In conclusion, the results demonstrate the genotoxic effect of potassium dichromate in mice. The results also confirm the protective role of thiola and soybean seeds against the genotoxicity of potassium dichromate.

Evaluation of genotoxic and cytotoxic potential of thiola (N-2-mercaptopropionylglycine), a medicine used in the treatment of humans contaminated with mercury

In Brazil, environmental contamination by mercury occurs mainly as a result of gold mining activities, especially in the Amazon region. In this area, human contamination results mainly from consumption of fish. Treatment of current symptoms of acute or chronic mercury contamination is normally carried out by increasing its excretion through metal scavenger compounds. In Japan, human contamination by mercury, which causes Minamata disease, has been successfully treated by the metal scavenger thiola (N-2 mercaptopropionylglycine). Its effects are based on its capacity to couple with the metal, facilitating its excretion. The possible clastogenic or anticlastogenic effect of thiola was evaluated by the in vivo micronucleus study in bone marrow erythrocytes of mice and also in human lymphocytes in vitro through chromosomal aberration analysis. In both experiments, different concentrations of thiola were used. Treatments with bleomycin (BLM), cyclophosphamide (CP), and also treatments combining these drugs with thiola were carried out with the purpose of studying the anticlastogenicity of thiola, considering its antioxidant properties. Thiola did not induce a significant increase in the micronucleus frequency in polychromatic erythrocytes of mice nor show any protective effect on the damage caused by bleomycin and cyclophosphamide in these cells. At a high dose, thiola showed a cytotoxic effect, significantly decreasing the relative proportion of polychromatic erythrocytes. In human lymphocytes, the tested drug did not increase the frequency of chromosomal aberration and also did not have any protective effect on the damage caused by BLM and CP.

X-irradiation of G1 CHO cells induces SCE which are both true and false in BrdU-substituted cells but only false in biotin-dUTP-substituted cells

The SCE-test is widely used in genetic toxicology and therefore knowledge of the contribution of BrdU to the formation of spontaneous and induced SCE is of great importance. The present study was undertaken to analyse the role of BrdU in X-ray-induced SCE. If SCE resulted from inversions, rings and double minutes (RDM) would be the asymmetrical counterparts of SCE and should therefore have the same frequencies. Dose-effect relationships of SCE and RDM show that the frequencies of SCE are much higher than those of RDM. We conclude that only a few SCE may represent inversions. In a second set of experiments, endoreduplications were induced in cells irradiated either before or after labelling with BrdU. Analysis of SCE in endoreduplicated chromosomes allows the discrimination of the cell cycle in which they originated. The results show that SCE are only induced in the first cell cycle following irradiation of BrdU-substituted cells, indicating that labelling with BrdU is a necessary prerequisite for the formation of SCE. In order to test this directly, radiation-induced SCE frequencies were studied in cells prelabelled with BrdU or biotin-dUTP in a third set of experiments. The structure of biotin-dUTP suggests that, in contrast to BrdU, it does not give rise to radicals during irradiation. Significantly lower frequencies of SCE were observed in biotin-dUTP-substituted cells than in BrdU-labelled cells. Calculations show that nearly all SCE induced in biotin-dUTP-labelled chromosomes can be explained by chromosomal aberrations (false SCE). In contrast to this, most SCE induced by X-rays in BrdU-labelled cells are not due to chromosomal aberrations, but result from S-dependent lesions (true SCE). This clearly points towards radiation damage in BrdU-moieties as the source of DNA lesions leading to SCE.